Systems and methods for measuring drivetrain power transmission

ABSTRACT

Power transmitted from a cyclist to a bicycle through crank arms is indirectly measured by performing calculations on direct physical measurements. The direct physical measurements are taken from sensors that can be non-rotationally coupled to the frame of the bicycle. The sensors can be integrated into the frame or installed as a module within a standard, unmodified bicycle bottom bracket. Measured power can be viewed by the cyclist using a wirelessly connected user interface device.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to U.S. Nonprovisionalapplication Ser. No. 15/619,543, entitled “SYSTEMS AND METHODS FORMEASURING DRIVETRAIN POWER TRANSMISSION,” filed Jun. 12, 2017, and toU.S. Provisional Application No. 62/348,310, entitled “DRIVETRAIN LOADSENSING APPARATUS”, filed Jun. 10, 2016, each of which is herebyincorporated by reference in its entirety for all purposes.

BACKGROUND Field

This non-provisional U.S. patent application relates generally tomechanical torque and power measurement and more specifically to asystems and methods for measuring drivetrain power transmission.

Description of Related Art

Bicycles are a popular type of transportation device. A bicycle isgenerally constructed to include a pair of wheels, a frame, a seat,handlebars, a steering mechanism, and a drivetrain. The drivetraingenerally includes a crank assembly, a power transfer element, and atransmission element that allows a cyclist to adjust a drivetrain ratio(gear ratio). The crank assembly typically includes two pedals used by acyclist to couple rotational power to the drivetrain.

While riding a bicycle, a cyclist typically transmits rotational powerto the bicycle through the crank assembly. In certain trainingscenarios, quantifying the rotational power is useful for tracking andimproving cyclist performance. In other scenarios, quantifyingrotational power is useful for controlling power output of motorizedrider assist systems. For example, a motorized rider assist system caninclude a battery, an electric motor that is coupled to the drivetrain,and a controller that adjusts power to the electric motor in proportionto rotational power provided by the cyclist.

Certain conventional techniques perform a direct strain or loadmeasurement on drivetrain elements that move relative to the bicycleframe. Such techniques require signal transmission between movingdrivetrain elements and the bicycle frame, thereby reducing overallreliability while increasing cost and system complexity. Otherconventional techniques fail to accurately measure power transmittedfrom the cyclist to the drivetrain, limiting usefulness in certainapplications. Thus, there is a need for addressing these issues and/orother issues associated with the prior art.

SUMMARY

According to various embodiments, a system, comprising: a measurementside inner bearing cup having an outside diameter, configured to fitwithin a measurement side outer bearing cup having an inside diameter,wherein an open volume is formed between the outside diameter of themeasurement side inner bearing cup and the inside diameter of themeasurement side outer bearing cup; a first load sensor, coupled to themeasurement side inner bearing cup at a first position along the outsidediameter and within the open volume, wherein the first load sensor isconfigured to provide a first analog electrical signal responsive to afirst applied force; a presence sensor configured to generate adetection signal in response to detecting proximity to a detectionfeature; an analog-to-digital converter configured to sample the firstanalog electrical signal into corresponding digital values; and amicroprocessor coupled to the analog-to-digital converter and thepresence sensor, and configured to: generate a force value correspondingto one of the digital values; generate a rotational position value usingthe detection signal; generate rotational velocity value using thedetection signal; calculate a torque value by dividing a first productof multiplying the force value with a length value for a crank arm by asine function of the rotational position; and calculate a power value bymultiplying the torque value with the rotational velocity value.

According to various further embodiments, a method comprising:converting, by a power measurement system, a first analog electricalsignal provided by a first load sensor into corresponding digitalvalues, wherein the first analog electrical signal is response to anapplied force; generating, by the power measurement system, a forcevalue corresponding to one of the digital values; generating, by thepower measurement system, a rotational position value by countingdetection signals from a presence sensor, which is configured to detectrotational position changes; generating, by the power measurementsystem, a rotational velocity value by measuring arrival time intervalsfor the detection signals; calculating, by the power measurement system,a torque value by dividing a first product of multiplying the forcevalue with a length value for a crank arm by a sine function of therotational position; and calculating, by the power measurement system, apower value by multiplying the torque value with the rotational velocityvalue.

According to various still further embodiments, a system comprising: ameasurement side inner bearing cup having an outside diameter,configured to fit within a measurement side outer bearing cup having aninside diameter; a first strain block, coupled to the measurement sideinner bearing cup at a first position along the outside diameter and theinside diameter of the measurement side outer bearing cup; a firststrain gauge, coupled to the first strain block, wherein the firststrain gauge is configured to provide a first analog electrical signalresponsive to a first applied force; a presence sensor configured togenerate a detection signal in response to detecting proximity to adetection feature; an analog-to-digital converter configured to samplethe first analog electrical signal into corresponding digital values;and a microprocessor coupled to the analog-to-digital converter and thepresence sensor, and configured to: generate a force value correspondingto one of the digital values; generate a rotational position value usingthe detection signal; generate rotational velocity value using thedetection signal; calculate a torque value by dividing a first productof multiplying the force value with a length value for a crank arm by asine function of the rotational position; and calculate a power value bymultiplying the torque value with the rotational velocity value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a bicycle frame bottom bracket area in which variousembodiments can be practiced.

FIG. 2A is an exploded view of a power measurement system, according tosome embodiments.

FIG. 2B is an exploded view of a power measurement system withnon-rotating components clustered separately from rotating components,according to some embodiments.

FIG. 3A is a partial section view of a power measurement system,according to some embodiments.

FIG. 3B is a partial side view of a power measurement system, accordingto some embodiments.

FIG. 4 illustrates a crank sensor assembly, according to someembodiments.

FIG. 5A is a detailed view of a bearing sensor assembly, according tosome embodiments.

FIG. 5B is a detailed view of an alternative bearing sensor assembly,according to some embodiments.

FIG. 6 illustrates a sensor array configuration for a power measurementsystem, according to some embodiments.

FIG. 7 illustrates an exemplary sensor calibration curve, according tosome embodiments.

FIG. 8 is a plot of exemplary force measurements sampled from four loadsensors during sequential crank rotations, according to someembodiments.

FIG. 9 is a plot of exemplary angular position samples taken duringsequential crank rotations, according to some embodiments.

FIG. 10 illustrates exemplary angular velocity samples measured fromangular position data, according to some embodiments.

FIG. 11 illustrates exemplary measured power values, according to someembodiments.

FIG. 12 illustrates a comparison between power values measured usingtechniques disclosed herein and directly measured power from acalibrated dynamometer, according to some embodiments.

FIG. 13 illustrates a crank and chainring free-body diagram forcalculating torque about a bottom bracket bearing axis, according tosome embodiments.

FIG. 14 illustrates an alternative free-body diagram, according to someembodiments.

FIG. 15 illustrates an electronic system configured to perform one ormore techniques disclosed herein, according to some embodiments.

FIG. 16 is a flow chart of a method for measuring power transmitted to adrivetrain, according to some embodiments.

DETAILED DESCRIPTION

Systems and methods for measuring drivetrain power transmission aredisclosed. The systems and methods can be implemented within the frameof a bicycle to measure power transmission from a cyclist to thebicycle. In one embodiment, a power measurement system is mounted withina bicycle bottom bracket shell of a bicycle frame, with physical sensorsadvantageously mounted in fixed, non-rotating positions relative to thebicycle frame. The physical sensors include a set of load sensors and aHall Effect sensor provide physical measurement signals that can besampled and combined to calculate a real-time measure of powertransmission. In one embodiment, the power measurement system isintegrated and assembled into a bicycle bottom bracket. In anotherembodiment, the power measurement system is integrated into a bottombracket shell, as part of a bicycle frame. In yet another embodiment,the power measurement system is fabricated into a cartridge or modulethat can be installed into a standard, unmodified bicycle bottombracket. In certain embodiments, the power measurement system includescircuitry for wirelessly transmitting, without limitation, measuredpower values to a user interface device for display to the cyclist.

The set of load sensors and the Hall Effect sensor provide requisitephysical measurement signals to calculate power transmission. In certainembodiments, measured power transmission is displayed to the cyclist inreal-time and/or recorded for later viewing, such as for trainingpurposes. In certain other embodiments, measured power is used tocontrol a motorized assist system coupled to the drivetrain. In oneembodiment, power values are calculated by multiplying a torque valueapplied to the drivetrain within a time interval by a rotationalvelocity value of the drivetrain calculated for the time interval.

FIG. 1 illustrates a bicycle frame bottom bracket area 100 in whichvarious embodiments can be practiced. As shown, a bottom bracket shell105 is coupled to a frame down tube 102, a seat post tube 103, chainstay tubes 104, two crank arms 101, and a drive sprocket 106. Otherbicycle components used to construct a complete bicycle are not shownherein.

In one embodiment, components comprising a power measurement systemdisclosed herein are mounted within the bottom bracket shell 105. Incertain embodiments, a bearing cup (not shown) is disposed at each oftwo opposite ends of bottom bracket shell 105, and a bearing (not shown)is inserted into, such as by press fitting, the bearing cups, enclosingthe power measurement system within the bottom bracket shell 105.

FIG. 2A is an exploded view of a power measurement system 200, accordingto some embodiments. As shown, power measurement system 200 comprises adrive side bottom bracket bearing 201, a drive side inner bearing cup202, an inner sleeve 203, a drive side outer bearing cup 204, acrank-position sensor sleeve 205, a non-drive side bearing cup 206, anon-drive side bottom bracket bearing 211, a logic board 207, loadsensors 208, a battery 209, and magnets 212. In one embodiment, powermeasurement system 200 is coupled to a crank spindle 210. In analternative embodiment, power measurement system 200 includes crankspindle 210. In certain embodiments, power measurement system 200 isdisposed within bottom bracket shell 105. In one embodiment, powermeasurement system 200 further includes a display unit (a user interfacedevice) configured to display measured power.

First crank arm 101 on a drive side and second crank arm 101 at anon-drive side, crank spindle 210, and drive sprocket 106 togethercomprise a crank assembly. A crank arm 101 is coupled to each opposingend of crank spindle 210. A pedal is rotationally coupled to each crankarm 101. In one embodiment, a cyclist is able to exert a power strokeusing their right leg against a pedal coupled to the crank arm 101 onthe drive side. Subsequently, the cyclist is able to exert a powerstroke using their left leg against a pedal coupled to the crank arm 101on the non-drive side, and so forth in alternating power strokes. Inalternative embodiments, drive sprocket 106 and drive side are disposedat the left side of the cyclist and the non-drive side is disposed atthe right side of the cyclist. Each power stroke transmits power fromthe cyclist to a crank arm 101, and crank spindle 210, which transmitsthe power to drive sprocket 106. In one embodiment, drive sprocket 106includes teeth configured to mesh with and transmit power from the powerstrokes to a chain, which further transmits the power to a rear wheel ofa bicycle. In this way, the cyclist is able to provide rotational powerat the rear bicycle wheel for propelling the bicycle forward.

In one embodiment, bearing loads are measured nearest the drive sideusing four load sensors 208. Load sensors 208 are radially mounted in anopen volume (e.g., an annulus volume) between drive side outer bearingcup 204 and drive side inner bearing cup 202. In other embodiments,bearing loads are measured using fewer than four or more than four loadsensors 208. In an alternative embodiment, bearing loads are measured atthe non-drive side. In such an embodiment, the structure of powermeasurement system 200 can be substantially preserved but with certaindrive side and non-drive side components reversed, so that load sensors208 are configured to measure bearing load at the non-drive side (awayfrom drive sprocket 106).

Drive side inner bearing cup 202 includes a first inside bore configuredto accept an outer race of drive side bottom bracket bearing 201. Driveside inner bearing cup 202 also includes an outside diameter to supportan inner surface of load sensors 208. A second inside bore of drive sideinner bearing cup 202 supports the drive side of inner sleeve 203. Inone embodiment, drive side inner bearing cup 202 includes a firstflanged lip that registers against drive side outer bearing cup 204 toprovide axial positioning.

In one embodiment inner sleeve 203 provides a mounting surface for logicboard 207 and battery 209. Inner sleeve 203 is coupled to drive sideinner bearing cup 202. Furthermore, inner sleeve 230 is configured toslide inside non-drive side bearing cup 206 and can be sealed with ano-ring (not shown). In alternative embodiments, logic board 207 and/orbattery 209 are mounted elsewhere. Battery 209 may be a standard coincell battery, or rechargeable battery such as a lithium ion battery.Furthermore, battery 209 can be mounted externally for ease ofreplacement. In one embodiment, battery 209 is mounted within astructural tube (e.g., bicycle frame down tube 102, bicycle frame seattube 103, bicycle frame chain stay 104) comprising the bicycle frame.

In one embodiment, drive side outer bearing cup 204 accepts an outersurface of load sensors 208, and an outside diameter of drive side outerbearing cup 204 fits inside bottom bracket shell 105. Drive side outerbearing cup 204 includes a second flanged lip that provides axialalignment with a first flanged lip on drive side inner bearing cup 202.A second flanged lip also seats against bottom bracket shell 105.

In one embodiment, crank position sensor sleeve 205 is configured to fitwithin an inside diameter of an inner race of drive side bottom bracketbearing 201. Crank position sensor sleeve 205 is configured to slideover crank spindle 210. In one embodiment, crank position sensor sleeve205 has eight evenly spaced radial holes. The radial holes areconfigured to each hold a magnet 212 radially positioned around crankspindle 210. Magnets 212 can be molded, glued, pressed into, orotherwise coupled to crank position sensor sleeve 205. A hole fabricatedin inner sleeve 203 allows a Hall

Effect sensor (not shown) to be positioned close to magnets 212. Crankposition sensor sleeve 205 includes a third flanged lip, configured toposition crank position sensor sleeve 205 against drive side bottombracket bearing 201.

Non-drive side bearing cup 206 includes an inside bore to accept anouter race of non-drive side bottom bracket bearing 211. Non-drive sidebearing cup 206 fits within bottom bracket shell 105. A flange axiallypositions non-drive side bearing cup 206 with bottom bracket shell 105.Opposite the flange, non-drive side bearing cup 206 accepts inner sleeve203.

Crank spindle 210 is coupled to the two crank arms 101, which togetheror separately are coupled to drive sprocket 106. Crank spindle 210passes through non-drive side bottom bracket bearing 211, drive sidebottom bracket bearing 201, and crank position sensor inner sleeve 205.Both drive side bottom bracket bearing 201 and non-drive side bottombracket bearing 211 support crank spindle 210.

In one embodiment, logic board 207 includes a printed circuit board withsurface mounted components and multilayer interconnection traces. Logicboard 207 mounts to inner sleeve 203. Logic board 207 includes a HallEffect sensor 301 configured to face inner sleeve 203. In certainembodiments, Hall Effect sensor 301 is positioned at least partiallywithin a hole in inner sleeve 203, such that magnets 212 can be readilydetected as crank position sensor sleeve 205 rotates. As a magnet 212approaches, Hall Effect sensor 301 detects a magnetic field from themagnet 212 and generates a detection signal (e.g., a pulse or other formof signal). Interconnecting wires are routed between logic board 207 theload sensors 208. In certain embodiments, the interconnecting wires arefabricated onto a flexible circuit interconnect (e.g., flex cable).Logic board 207 receives and processes cyclist inputs, programminginputs, and electrical signals from load sensors 208, and Hall Effectsensor 301 to calculate power measurement data, such as real-time powergenerated by a cyclist. In certain embodiments, logic board 207 isconfigured to transmit data wirelessly to a head unit (user interfacedevice), which displays the data to the cyclist. In one embodiment,battery 209 provides power to the electronics contained in the bicyclebottom bracket assembly (e.g., circuitry on logic board 207), and mountsto inner sleeve 203. While various embodiments described herein refer tomagnets 212 and Hall Effect sensor 301, any presence sensor (e.g., HallEffect sensor, inductive sensor, optical sensor, etc.) can beimplemented instead. In general, a presence sensor detects proximity ofa physical detection feature. For example, a magnetic presence sensorsuch as a Hall Effect sensor or inductive sensor (e.g., a coil) detectsthe proximity of a magnetic field (detection feature) generated by amagnet 212 when the magnet 212 is brought into proximity of the magneticpresence sensor. In another example, an optical sensor detects anoptical mark such as a reflective surface (detection feature) broughtinto proximity of the optical presence sensor.

FIG. 2B is an exploded view of power measurement system 200 withnon-rotating components clustered separately from rotating components,according to some embodiments. In one embodiment, the rotatingcomponents include crank spindle 210, crank arms 101, drive sprocket106, crank position sensor sleeve 205, drive side bottom bracket bearing201, and magnets 212. Furthermore, the non-rotating components includelogic board 207, battery 209, drive side inner bearing cup 202, innersleeve 203, drive side outer bearing cup 204, non-drive side bearing cup206, non-drive side bottom bracket bearing 211, and bottom bracket shell105.

FIG. 3A is a partial section view of power measurement system 200,according to some embodiments. As shown, crank spindle 210 is coupled tocrank position sensor sleeve 205. Magnets 212 are coupled to crankposition sensor sleeve 205. In one embodiment, eight magnets 212 arecoupled to crank position sensor sleeve 205 and evenly positioned atforty-five degree intervals about crank position sensor sleeve 205.During assembly, crank spindle 210 is inserted through two bearingsincluding drive side bottom bracket bearing 201 and non-drive sidebottom bracket bearing 211. The two bearings allow crank spindle 210 torotate freely in place about central axis 302, while drive side bottombracket bearing 201 is subjected to transient linear forces due to acyclist power stroke. The transient vertical bearing reaction forcevalues are measured by load sensors 208, while rotational position(angular position) values and rotational velocity (angular velocity)values are calculated from signals generated by Hall Effect sensor 301.Torque is calculated from the vertical bearing reaction force values incombination with rotational position values. Power values are calculatedby multiplying calculated torque values with rotational velocity values.For example, in a specific time interval, a vertical bearing reactionforce value is measured, a rotational position value measured, and arotational velocity value is measured. The vertical bearing reactionforce is measured by quantizing an electrical load sensor signal usingan analog-to-digital converter (ADC). The rotational position value ismeasured counting a detection signal from Hall Effect sensor 301, andthe rotational velocity value is measured as a function of arrival timeintervals for the detection signals.

In one embodiment, components of power measurement system 200 arecoupled to a bicycle frame and do not rotate or move with respect to thebicycle frame. In certain embodiments, power measurement system 200 ismanufactured to be an integral part of the bicycle frame. For example,power measurement system 200 can be integrated into bicycle bottombracket shell 105. In other embodiments, power measurement system 200 isconfigured to be a module or cartridge that can be optionally coupled tothe bicycle frame, such as by inserting the module or cartridge intobicycle bottom bracket shell 105.

FIG. 3B is a partial side view of power measurement system 200,according to some embodiments. As shown, crank spindle 210 is alignedalong central axis 302 when inserted into power measurement system 200.In one embodiment, a crank sensor assembly (e.g., crank sensor assembly400 of FIG. 4) is configured to measure a rotational position values forcrank spindle 210, and a bearing sensor assembly (e.g., bearing sensorassembly 500 of FIG. 5A) is configured to measure vertical force valuesapplied to bearings (vertical bearing reaction) within power measurementsystem 200.

FIG. 4 illustrates a crank sensor assembly 400, according to someembodiments. In one embodiment, crank sensor assembly 400 is configuredto measure rotational position of crank spindle 210. Crank sensorassembly 400 includes Hall Effect sensor 301, crank position sensorsleeve 205, and eight magnets 212 evenly spaced around the perimeter ofcrank position sensor sleeve 205. In one embodiment, Hall Effect sensor301 is mounted to logic board 207. In other embodiments, Hall Effectsensor 301 is coupled to logic board 207 through electricalinterconnects, such as wires or a flex cable.

In one embodiment, eight magnets 212 are mounted within holes that arefabricated to be evenly spaced around the perimeter of crank positionsensor sleeve 205. Crank position sensor sleeve 205 rotates with aninner race of drive side bottom bracket bearing 201. Drive side bottombracket bearing 201 is mounted in drive side inner bearing cup 202,which is not shown for clarity in FIG. 4. Crank spindle 210 can bepositioned for operation by sliding through crank position sensor sleeve205. Crank spindle 201 is connected to crank arms 101. This completeassembly rotates with crank spindle 210 as the cyclist pedals crank arms101.

In one embodiment, a calibration position is established by orientingcrank position sensor sleeve 205 relative to a crank arm 101. Ingeneral, crank arms 101 can be aligned to bisect two magnets. Positionis determined as crank position sensor sleeve 205 rotates with crank arm101 and crank spindle 210, causing magnets 212 to travel past HallEffect sensor 301. A new rotational position value for crank spindle 210is detected as a magnet 212 passes sufficiently close (next to) HallEffect sensor 301. In one embodiment, Hall Effect sensor 301 and logicboard 207 are fixed to inner sleeve 203 (not shown in FIG. 4 forclarity).

FIG. 5A is a detailed view of a bearing sensor assembly 500, accordingto some embodiments. In one embodiment, bearing sensor assembly 500includes four load sensors 208, spaced evenly around an open volume(e.g., annulus volume) between drive side inner bearing cup 202 anddrive side outer bearing cup 204. Additionally, drive side inner bearingcup 202 supports drive side bottom bracket bearing 201. The drive sideouter bearing cup 204 is pressed into frame bottom bracket shell 105.Applied loads from either crank arm 101 are detected by load sensors208. Using crank spindle 210 position and crank spindle 210 velocitymeasurements, the contributions from crank arms 101, and therefore, eachcyclist leg can be separately calculated. In certain embodiments, driveside inner bearing cup 202 and drive side outer bearing cup 204 includemutually-parallel flat sections that span portions of respectiveperimeter geometry. In such embodiments, load sensors 208 can befabricated to be substantially planar and are mounted within an openvolume formed between the flat (planar) sections.

In one embodiment, load sensors 208 comprise thin film load sensors.Conventional thin film load sensors include a resistive elementlaminated between two plastic films, with the resistive elementconfigured to exhibit higher electrical resistance in an unloaded stateand decreasing resistance as load increases. Conventional thin film loadsensors are generally not completely linear in their electrical responseto applied force. To account for any nonlinearity, a formula or look uptable can be used to map a measured electrical (e.g., resistance) valueto a force value.

In an exemplary calibration process, known loads within an anticipatedoperating range are applied to a load sensor 208, and corresponding ADCoutputs are recorded to generate a sensor calibration curve. In oneembodiment, power measurement system 200 is coupled to a dynamometer andsubjected to a range of different mechanical torque and/or velocity andpower inputs. Measurement data from the dynamometer can be recorded asphysically accurate reference data in conjunction with direct sensormeasurement data from power measurement system 200. In such anembodiment, the sensor calibration curve is defined by a correlationbetween the direct sensor measurement data and the physically accuratereference data. A sample sensor calibration curve is plotted in FIG. 7,discussed further herein, which indicates measured force (load) as afunction of a measured ADC value. Formula coefficients can be calculatedto fit the plotted data using conventional curve-fitting techniques, ora lookup table can be generated based on measured calibration data.

Although a specific type load sensor is described herein, alternativeload sensor devices and/or electrical behavior of load sensor devicescan be implemented without departing from the scope and spirit ofembodiments of the present disclosure. One exemplary conventional thinfilm load sensor is manufactured by Tekscan® under the product nameFlexiforce™ A201. This product is approximately one hundredth of an inch(0.010″) thick and provides suitable sensitivity over a force rangecorresponding to a power stroke generated by a human pressing against abicycle pedal.

FIG. 5B is a detailed view of an alternative bearing sensor assembly550, according to some embodiments. As shown, an outer bearing cup 552is coupled to an inner bearing cup 554 through a strain block 562. Astrain gauge 560 is coupled to strain block 562 and configured tomeasure strain exhibited by strain block 562. In one embodiment, straingauge 560 is responsive to directionally specific strain. In oneembodiment, outer bearing cup 552 is drive side outer bearing cup 204and inner bearing cup is drive side inner bearing cup 202. In such anembodiment, strain gauge 560 is responsive to bearing reaction forcevalues, such as bearing reaction force values measured by load sensors208. In this way, strain gauges 560, coupled to strain blocks 562, canbe substituted for load sensors 208. In one embodiment, strain block 562is fabricated as a discrete component and configured to couple outerbearing cup 552 to inner bearing cup 554. In an alternative embodiment,strain block 562 is fabricated as part of a single component thatincludes outer bearing cup 552 and inner bearing cup 554.

FIG. 6 illustrates a sensor array configuration 600 for bearing sensorassembly 500, according to some embodiments. In one embodiment, bearingsensor assembly 500 includes four load sensors 208, spaced evenly arounda measurement perimeter 610 that corresponds to an outer perimeter ofdrive side inner bearing cup 202. For reference, an x-axis 601 and ay-axis 602 are shown within a plane that is perpendicular to centralaxis 302. A sensor 208 is located at positions shown as A, B, C, and D.In certain embodiments, bearing sensor assembly 550 is configuredaccording to sensor array configuration 600, with strain gauges 560disposed in positions A, B, C, and D.

In one embodiment, logic board 207 includes an ADC, configured tomeasure force at load sensors 208. To measure force at a load sensor208, an electrical value from the load sensor 208 is sampled by the ADCto generate a digital value, which is mapped to a measured force valueusing an equation with calibrated coefficients or a lookup tablecomprising calibration measurements for the load sensor 208. In oneembodiment, the equation is used to calculate a force value using thedigital value as an input variable. In another embodiment, the digitalvalue is used as a lookup index into the lookup table (or other datastructure), which provides a force value output.

Load sensors 208 are generally designed to measure compressive loads.However, some tensile load can be detected as a preload is removed froma particular sensor. Applying a load to the crank assembly in thedirection of a particular load sensor 208 (for example, load sensor 208at location A) slightly shifts drive side inner bearing cup 202 in thatdirection. This shift removes preload on the opposite load sensor 208(for example, load sensor 208 at location sensor C), which reads astensile force measured. The detectable range of tensile force is limitedto the preload in bearing sensor assembly 500; thus, the primary purposeof load sensors 208 is to measure compressive load in a particulardirection.

FIG. 7 illustrates an exemplary sensor calibration curve, according tosome embodiments. A force, measured in pounds (lbs), applied to loadsensor 208 can produce a non-linear electrical response, which resultsin an ADC digital output value (e.g., ADC value) having a non-linearrelationship to the applied force. The non-linear relationship can beaccounted for using the sensor calibration curve. For example, a forceapplied to a load sensor 208 results in a particular ADC value,indicated along the horizontal axis of a sensor calibration curve. ThisADC value maps directly to a measured force value, indicated along thevertical axis, through the sensor calibration curve. Discretecalibration points (e.g., shown here at zero pounds, fifty pounds, onehundred pounds, and so forth) can be determined for a particular loadsensor 208 during a calibration operation. The discrete calibrationpoints establish a sensor calibration curve over an operational rangefor load sensor 208.

In one embodiment, the sensor calibration curve is represented as a setof coefficients that are curve fit to an appropriate calibration curveequation. A given ADC value measured from a load sensor 208 can be usedas an input variable to the calibration curve equation to calculate ameasured force value. In other embodiments, the sensor calibration curveis represented as a set of lookup table entries. A given ADC value isused as an index into the lookup table. In certain embodiments,interpolation can be performed between different lookup table entriesfor higher resolution. For example, higher-order bits of an ADC valuecan be used as a lookup table index, while lower-order bits of the ADCvalue can be used to provide an interpolation weight between lookuptable values.

Data measured and plotted for an exemplary test scenario are given inFIGS. 8 through 12. The data plotted in FIG. 8 through FIG. 12 weremeasured during the same time interval where a cyclist was beginning topedal from a resting position (zero rotational velocity).

FIG. 8 is a plot of exemplary force measurements sampled from four loadsensors 208 during sequential crank rotations, according to someembodiments. In one embodiment, the force measurement values arecalibrated according to a sensor calibration curve. As shown, measuredforce exhibits a cyclic trend consistent with each revolution of thecrank assembly as the cyclist pedals at increasing rotational velocity.

Larger peak loads are present at sensors A and B since chain force ortension in the chain results in compressive load at sensors A and B.Although similar tensile load would be expected at sensors C and D,specific construction details of this exemplary implementation limit thedevices ability to measure tensile load.

FIG. 9 is a plot of exemplary angular position sensor readings sampledduring sequential crank rotations, according to some embodiments.Rotational position is labeled with respect to eight different rotationdetection points 910 or crank octants, corresponding to each of eightdifferent magnets 212. At detection point 910(0) a first of magnets 212is aligned with Hall Effect detector 301, triggering a detection signalfrom Hall Effect detector 301 that indicates crank spindle 210 isrotated to zero degrees in a rotation path of crank spindle 210. Atdetection point 910(1), a second of magnets 212 is aligned with HallEffect detector 301, indicating crank spindle 210 is rotated toforty-five degrees, and so forth. At detection point 910(7), crankspindle 210 is rotated to three-hundred fifteen degrees. The nextforty-five degrees of rotation returns the crank spindle 210 to zerodegrees of rotation. As crank spindle 210 rotates, magnets 212 aresuccessively detected by Hall Effect detector 301. As successivedetection signals are received by circuitry within logic board 207, arotational position register (e.g., a counter) is incremented, startingat zero and wrapping around back to zero after a count of seven.

In one embodiment, the angular (rotational) position is measured using asingle Hall Effect sensor 301 that detects proximity of a magnetic fieldduring rotation of a series of eight magnets 212, which are spacedevenly around crank position sensor sleeve 205. Starting from a knownhome position, with the crank horizontal (in octant 0), circuitry withinlogic board 207 tracks magnets 212 as they pass Hall Effect sensor 301.The circuitry updates a current angular position for crank spindle 210and therefore crank arms 101. In one embodiment, software executing on aprocessor on logic board 207 increments the angular position of crankarms 101 each time a magnet 212 is detected by Hall Effect sensor 301,returning the angular position back to zero upon completing a fullrotation. As the crank velocity increases, slope of the angular positioncurve becomes steeper. Any technically feasible technique can beimplemented to detect a zero rotation position/orientation, includinginterpolating between peak force values (occurs when crank arms 101 arehorizontal).

In one embodiment, the cyclic nature of the load sensor data is used todetermine the orientation of the bottom bracket. In light of theteachings provided herein, persons of ordinary skill in the art willunderstand that various algorithms can be configured to detect peakforce and corresponding rotational positions (phase) on each of the loadsensors 208. Using the peak load phase, an orientation of the loadsensor array can be determined with respect to the chain force and crankarm position. In this way, rotational position can be determineddynamically. Furthermore, time intervals measured between detected peakscan be used to determine angular velocity. In one embodiment, areciprocal function of duration for each time interval provides averageangular velocity during the time interval. In another embodiment, anaverage frequency of a signal generated using detected peaks provides anaverage angular velocity.

FIG. 10 illustrates exemplary angular velocity measured from angularposition data sampled during sequential crank rotations, according tosome embodiments. In one embodiment, logic board 207 is configured tocalculate angular velocity for crank spindle 210 based on a signal fromHall Effect sensor 301. Angular velocity is proportional to the angulardistance between magnets 212, divided by the time passage between magnet212 detections at Hall Effect sensor 301. Consequently, an updatedreal-time angular velocity value can be calculated each time a magnet isdetected as a direct function of time passage from the previous magnetbeing detected.

FIG. 11 illustrates exemplary measured power values, according to someembodiments. The measured power values are calculated using underlyingphysical measurements of force values, position values, and rotationalvelocity values that are sampled during sequential crank rotations. Inone embodiment, power is calculated according to Equation 1.

Power=Torque×Velocity   (Equation 1)

In one embodiment, the torque variable of Equation 1 is calculated asdescribed herein using force measurements from load sensors 208, and thevelocity variable is calculated using time intervals between successivemagnet detection events at Hall Effect sensor 301.

In one embodiment, mechanical power is transmitted through thedrivetrain and indirectly measured using the angular velocity of thecrank spindle 210 (which is the same for all rotating parts 101, 106,205, 210, 212) in combination with the moment (torque) applied to thedrive sprocket 106 by the chain force. However, the torque is alsoindirectly measured using a simplified force balance of the crank andbottom bracket assembly. The simplified force balance requires that allforces applied to the bottom bracket assembly must be balanced. Forcebalance at the bottom bracket assembly is illustrated in FIG. 13.

FIG. 12 illustrates a comparison between power values measured usingtechniques disclosed herein and directly measured power from acalibrated dynamometer, according to some embodiments.

In one embodiment, power is measured using techniques disclosed hereinto produce sequential power values. The sequential power values are thenfiltered using, for example, a conventional second order Butterworthfilter to produce a smoother, more representative power output, shown inthe upper plot (Filtered BB Power). Readings from a dynamometer in thesame system are shown in the lower plot (Raw Dyno Power). As shown, thefiltered plot in the upper graph is more intuitive and representative ofcyclist power output and effort.

FIG. 13 illustrates a crank and chainring free-body diagram 1300 forcomputing torque about a bottom bracket bearing axis (central axis 302),according to some embodiments. A three-dimensional assembly comprisingdrive side bottom bracket bearing 201, non-drive side bottom bracketbearing 211, and crank arms 101 coupled to crank spindle 210 simplify toform a two-dimensional free-body diagram, as depicted by free-bodydiagram 1300.

A plane is defined by x-axis 601 and y-axis 602, with a central axis 302(not shown) orthogonally intersecting at the intersection point ofx-axis 601 and y-axis 602 (origin). A chainring comprises teeth disposedaround the perimeter of drive sprocket 106, which is configured torotate about central axis 302. A chainring radius 1302 defines aneffective radius for the chainring. A crank arm length 1305 defines aneffective moment arm length for crank arms 101. A crank arm angle 1307defines an effective angle of rotation for a crank arm 101. In oneembodiment, crank arm angle 1307 corresponds to an angular position forcrank spindle 210. In certain embodiments, angular position is measuredwith respect to fixed components of an associated bicycle frame (e.g.,chain stay tubes 104). In other embodiments, angular position ismeasured with respect to a gravity vector. For example, a crank armangle 1307 of zero may be perpendicular to a gravity vector.

Forces operating within free-body diagram 1300 are shown to include,without limitation, pedal force 1306, vertical bearing reaction 1303,chain force 1301, and horizontal bearing reaction 1304. In oneembodiment, four load sensors 208 are configured to measure forcesapplied to crank spindle 210 relative to central axis 302. For examplevertical bearing reaction 1303 can be measured using the four loadsensors 208. Crank arm angle 1307 can be measured using the techniquesdisclosed herein, or any other technically feasible technique formeasuring a rotational angle.

Forces on each crank arm 101 are assumed to produce similar bearingreactions. Consequently, in one embodiment, only one crank arm 101 isconsidered in free-body diagram 1300.

Focusing on the vertical force balance, Equation 2 is obtained forcalculating torque due to a cyclist pressing on pedals attached to crankarms 101. Equation 2 makes three assumptions, including the chain forceacts in the horizontal direction, the pedal force acts perpendicular tocrank arm 101, and the crank assembly components have no inertia. In oneembodiment, torque is calculated according to Equation 2.

$\begin{matrix}{{{Torque} = {\frac{\mspace{14mu} \begin{matrix}{{Vertical}\mspace{14mu} {Bearing}} \\{Reaction}\end{matrix}}{\sin\begin{pmatrix}{\frac{\pi}{2} +} \\{\; \begin{matrix}{{{Crank}\mspace{11mu} {Arm}}\mspace{11mu}} \\{Angle}\end{matrix}}\end{pmatrix}}*{Crank}\mspace{11mu} {Arm}{\; \;}{Length}}}\;} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

Vertical bearing reaction 1303 (force) can be measured in real timeusing load sensors 208, real-time crank arm angle can be measured usingthe techniques disclosed herein or any other techniques. Crank armlength is typically a fixed value.

In one embodiment, circuitry comprising a microprocessor (ormicrocontroller) within logic board 207 is configured to cause forcemeasurements to be performed, such as by commanding an ADC (e.g., ADC1504 of FIG. 15) to digitize analog signals from load sensors 208 intocorresponding ADC samples (digital values). The microprocessor isconfigured to receive and process the ADC digital values into forcevalues using an appropriate sensor calibration curve, as describedherein. Furthermore, the microprocessor is configured to causerotational position measurements to be performed using Hall Effectsensor 301 and a rotational position register. Rotational positionvalues having eight different values (eight quantization levels) can beused directly from the rotational position register; however, additionalrotational position resolution can be obtained by interpolation for aspecific sample time. Additionally, the microprocessor is configured tocalculate torque values. In one embodiment the microprocessor calculatestorque values according to Equation 2, by plugging in the force valuesand the rotational position values. In one embodiment, themicroprocessor is further configured to calculate power according toEquation 1, using the calculated torque values and a rotational velocityvalue. In one embodiment, the rotational velocity value is calculatedusing a reciprocal function of time intervals between Hall Effect sensor301 detection signals generated at different rotation detection points910. In certain embodiments, software executing within themicroprocessor is configured to distinguish left from right leg powerbased on crank arm angle 1307. In one embodiment, software and/orfirmware is included in logic board 207 for processing data measureddata into usable cyclist information. For example, load sensor data andposition data can be processed into power output for a cyclist to read.

FIG. 14 illustrates an alternative free-body diagram 1400, according tosome embodiments. Alternative free-body diagram 1400 models greaterdetail compared to the simpler two-dimensional free-body diagram 1300presented in FIG. 13. In particular alternative free-body diagram 1400models crank arms 101, crank spindle 210 coupled to the crank arms 101,drive side bottom bracket bearing 201, and non-drive side bottom bracketbearing 211. Assumed in alternative free-body diagram 1400 is that thecyclist exerts pedal forces P1 or P2 perpendicularly to the crank arms101, that axial forces on crank spindle 210 can be neglected, and thatdrive sprocket 106 with applied chain force could be replaced by themoment (torque) T and horizontal force Ch_(y). As shown, R₁ is a crankarm 101 length, R₂ is the distance between drive side bottom bracketbearing 201 center and a chain line force in the x-direction, R₃ is thedistance between a non-drive side bottom bracket bearing 211 center anda center of the pedal force in the x-direction, and R₄ is the distancebetween a center of drive side bottom bracket bearing 201 and non-driveside bottom bracket bearing 211. Performing a force and moment balanceusing this diagram provides an alternative formula for relating thebearing loads to the chainring torque. The torque in this approach isgiven by Equation 3. The term B_(1Z) refers to a vertical (z-axis)bearing reaction force for a first bearing on the same side as P₁. Theterm and the term B_(1Y) refers to a horizontal (y-axis) bearingreaction force (e.g., along the direction for forward motion of abicycle) for the first bearing. Similarly, the term B_(2Z) refers to avertical bearing reaction force and the term B_(Y2) refers to ahorizontal bearing for a second bearing on the same side as P₂. Torqueis shown as T. This value of torque assumes the cyclist is applying apower stroke at P1. Crank arm angle is given by θ.

$\begin{matrix}{{Torque} = \frac{B_{1\; Z}{R_{4}\begin{pmatrix}{{R_{1}{\cos (\theta)}{\sin \left( {\frac{\pi}{2} + \theta} \right)}} -} \\{R_{1}\cos \; \left( {\frac{\pi}{2} + \theta} \right){\sin (\theta)}}\end{pmatrix}}}{{R_{3}{\sin \left( {\frac{\pi}{2} + \theta} \right)}} + {R_{4}{\sin \left( {\frac{\pi}{2} + \theta} \right)}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

In one embodiment, circuitry comprising a microprocessor (ormicrocontroller) within logic board 207 is configured to perform forceand rotational position measurements, as well as calculating torqueaccording to Equation 3 using the force and rotational positionmeasurements. In one embodiment, the circuitry is further configured tocalculate power in accordance with Equation 1, using the calculatedtorque from Equation 3 and a measured rotational velocity. In certainembodiments, software executing within the microprocessor is configuredto distinguish left from right leg power based on crank arm angle.

FIG. 15 illustrates an electronic system 1500 configured to perform oneor more techniques disclosed herein, according to some embodiments. Asshown, electronic system 1500 includes logic board 207 and load sensors208. Logic board 207 includes a wireless communication module 1502, HallEffect sensor 301, an onboard microprocessor 1503 (e.g., Atmel 328P), atemperature sensor 1506, and a load sensor amplifier and filter 1505. Inone embodiment, onboard microprocessor 1503 includes an onboard ADC1504. In another embodiment, ADC 1504 is implemented as a discretecircuit. ADC 1504 processes voltage signals from the load sensors 208and temperature sensor 1506 for use by microprocessor 1503. Load sensors208 and battery 209 are electrically connected to logic board 207, suchas by wires. In one embodiment, logic board 207, load sensors 208, andbattery 209 are contained inside the bicycle bottom bracket shell 105. Auser interface device 1501 is mounted separately outside of the bicyclebottom bracket shell 105. Wireless communication module 1502 on logicboard 207 communicates between logic board 207 and user interface device1501, for example to transmit a power value for display on userinterface device 1501. In one embodiment wireless communication moduleis configured to transmit measured real-time power values for display onuser interface device 1501.

Load sensor 208 resistance varies as a function of the applied load(force). Supplying load sensors 208 with a reference voltage allows thevoltage drop across the load sensors to be measured. In one embodiment,load sensor 208 outputs are amplified using an operational amplifieraccording to manufacturer's recommendations, with amplificationcontrolled using a digitally variable resistor, which can be set byonboard processor 1503. Onboard processor 1503 reads a load sensor 208and temperature sensor 1506 inputs by causing ADC 1504 to perform an ADCoperation. Load sensor 208 signals are used in power calculation by onboard processor 1503. Hall Effect sensor 301 output state is changed aseach magnet 212 on crank position sensor sleeve 205 passes the HallEffect sensor 301 location. As described in further detail herein, anoutput signal from Hall Effect sensor 301 is used for crank position andcrank velocity calculations necessary for power calculations by on boardprocessor 1503. In one embodiment, temperature sensor 1506 changesresistance as a function of the ambient temperature. Also using areference voltage, the voltage drop across the temperature sensor 1506can be measured by ADC 1504. Conventional load sensors 208 can varytheir output as a function of temperature. In one embodiment,temperature sensor 1506 signal information is used for calibration(temperature) compensation of the load sensor 208 signals. Variouscalibration curves, similar to FIG. 7, would be created in the desiredrange of operating temperatures. To calculate a load value (appliedforce) at a particular temperature, an interpolation would be performedusing the calibration curves and the temperature indicated bytemperature sensor 1506. In one embodiment, a first calibration curve isdefined for a first temperature and a second calibration curve isdefined for a second temperature. A given temperature value (e.g.,operating temperature for a load sensor 208) between the firsttemperature and the second temperature is used to interpolate between afirst force value provided by the first calibration curve and a secondforce value provided by the second calibration curve. The interpolationscheme could be nearest, linear, polynomial, or another similar method.In one embodiment, enclosed components 1510 are packaged within bicyclebottom bracket shell 105.

In one embodiment, user interface device 1501 is a separately powereddevice with a display screen and buttons for user input, as well aschanging display output. User interface device 1501 can be mounted onthe bicycle or on the cyclist. Existing user interface devices,including the Garmin™ Edge bicycling computers, can be integrated withand/or configured to operate with power measurement system 200. Powermeasurement system 200 can be configured to transmit digital data (e.g.,measured power values) wirelessly to the user interface device 1501. Thedata can be transmitted via Bluetooth, Low Energy Bluetooth, or ANT+protocols for example. The data transmitted can include cadence and/orpower output, calculated by power measurement system 200. User interfacedevice 1501 displays this data back to the user.

In certain embodiments, user interface device 1501 can be programmed toprovide multiple output display variations depending on the rider'spreference. These variations could be displayed in a user configuredlayout on the screen. Exemplary display variations include instantaneousor average right leg power output, instantaneous or average left legpower output, instantaneous total power, maximum power, and averagepower during a particular time interval. Display examples of cadencemeasurement include instantaneous cadence, peak cadence, and averagecadence during a particular time interval. Power measurement system 200can also be configured to receive data from user interface device 1501for setup or calibration.

In one embodiment, power measurement system 200 is installed in bicyclebottom bracket shell 105 of a bicycle frame in the same way typicalbottom bracket bearings 201 and 211, crank spindle 210, and crank arms101 are otherwise installed within a typical bottom bracket shell. Suchan installation requires orientation of load sensors 208 and Hall Effectsensor 301 with bicycle frame geometry and components. In thisembodiment, power measurement system 200 includes orientation alignmentmarkings for mounting power measurement system 200 with the load sensors208 and position Hall Effect sensor 301 in an appropriate orientationwith respect to frame geometry axis for proper power measurement. Crankarm 101 with crank spindle 210 is also aligned with a marking on crankposition sensor sleeve 205. Initial sensor preloads or offsets will becaptured automatically by the system on first power on and firstcommunication with the user interface. Such offsets can be used tocompensate future measurements.

Various embodiments advantageously provide for installation of powermeasurement system 200, to provide real-time power measurement, into thebicycle bottom bracket shell 105. Such installation can be performedwithout modification to existing crank parts or the bicycle frame. Thesystem measures left and right rider leg power output independently aswell as total rider power output, has wireless communication to a remoteuser interface device, and is mounted entirely inside the bicycle bottombracket. Alternatively, power measurement system 200 can positioncertain components (e.g., battery 209) external to bicycle bottombracket shell 105 to facilitate maintenance and/or ease of use.

In one embodiment, load sensors 208 are positioned to surround driveside bottom bracket bearing 201; however, other embodiments can includevarious combinations of load sensors 208 towards a drive side ornon-drive side bearing. In alternative embodiments load sensors 208 arepositioned surrounding the non-drive side, only surrounding the driveside, or surrounding the drive side and non-drive side.

In other embodiments, the load sensors are mounted between a bottombracket bearing and a bearing cup, between a bearing cup and a bicyclebottom bracket shell, between a bottom bracket bearing and a bicyclebottom bracket shell, or anywhere else in a bicycle bottom bracket areathat permits detection of the bearing loads.

In composite bicycle frames, the bottom bracket area is heavily filletedand the bottom bracket shell may not be as distinct as the hollowcylindrical shell depicted in this embodiment. In another embodiment,load sensors are embedded into the composite bicycle frame materialforming the bottom bracket shell area.

Alternative embodiments can include other load sensor types or designs.In certain embodiments, the load sensor 208 foot print or area requiredcan be customized for a particular application. Load sensors 208 can beput in places not normally accommodated by traditional direct loadsensing elements (e.g., load cells, strain gauges). The load sensor 208can be mounted on a curved surface as shown, or be placed on a machinedsurface or molded flat surface in the area of desired measurement. Thenumber of load sensors 208 can vary from a single load sensor to manyload sensors, or the load sensor could be a single continuous elementplaced in the open volume (e.g., annulus volume) between drive sideinner bearing cup 202 and drive side outer bearing cup 204.

When commercially available thin film type load sensors (e.g., TekscanFlexi Force A201) are installed on curved surfaces, the film layers tendto delaminate. The observed delaminating effects can be attributed toexcessive shear forces between the laminated layers. If the load sensorsare to be installed on curved surfaces and a long load sensor life isdesired, the plastic film should be formed to match the curved surfacebefore the resistive element is installed and the layers are laminatedtogether. Various methods could be used to form the plastic film tocurved surfaces including thermal forming and vacuum forming. Thesensing material can be applied before or after the film is formed.Using this method, installing the thin film load sensors on curvedsurfaces would not induce any shear force between the laminated layersthat could damage device integrity. In one embodiment, load sensors 208are thin film load sensors, fabricated to conform to a curved mountingsurface. For example, load sensors 208 can be fabricated to conform inshape to at least an arc section of the open volume between drive sideouter bearing cup 204 and drive side inner bearing cup 202. Whenassembled into place, the load sensors 208 can incur negligible initialloading (offsets). In such an embodiment, load sensors 208 can befabricated using any of the techniques discussed herein or any othertechnically feasible fabrication techniques. Of course, in certain otherembodiments flat mounting surfaces for load sensors 208 (e.g., facingsurfaces of drive side inner bearing cup 202 and drive side outerbearing cup 204) can be fabricated as discussed herein, and flat loadsensors 208 can be mounted to the flat mounting surfaces.

In one embodiment, power measurement system 200 is fabricated to operatein different bottom bracket configurations. More specifically, powermeasurement system 200 can be adapted to any bottom bracketconfiguration and size. In other embodiments, bottom bracket cups can beconfigured for various bottom bracket standards including threadedbottom bracket applications and various crank spindle standards. In yetother embodiments, various bearing configurations can be used, includingradial cartridge bearings, angular contact cartridge bearings, andtraditional cup/cone bearing assemblies.

In one embodiment, drive sprocket 106 includes teeth, configured to meshwith a sprocket engaging a chain (e.g., a bicycle chain), or similarpower transmission system. Furthermore, in alternative embodiments aconventional chain drive system comprising a sprocket and a chain isreplaced with other power transmission systems employing belts, cables,and/or other serpentine elements with no loss of applicability of powermeasurement system 200 described herein.

In other embodiments, various sensing techniques and detectable featuresmay be used for quantifying crank position. Such techniques can includeoptical sensor(s)/emitter(s) and associated detectable features,magnetic strip with alternating poles and associated sensor(s), orsensors to detect the movement of the ball bearings/bearing cage. In oneembodiment, a presence sensor is configured to detect proximity of anindividual ball (or balls) within a ball bearing. In such an embodiment,the detection feature comprises the individual ball or balls within theball bearing, and the presence sensor detects proximity of a ball. Anyunderlying physical proximity measurement can be performed to detectproximity of a ball. Such proximity measurement can include sensing anoptical, magnetic (e.g., field presence or permeability change),mechanical, or electrical physical property of the ball in proximity. Adetection signal from the presence sensor is used to measure angularposition and/or angular velocity. The presence sensor can be positionedat the outer race of the ball bearing and configured to detect proximityof a ball rolling by. A home position or calibration positionsensor/detectable feature may also be implemented using any of thepreviously described techniques or any other technically feasibletechniques.

In an alternative embodiment, Hall Effect sensor 301 and magnets 212 arereplaced with other features that can be detected optically.Alternatively, various other electronic sensors may be used to detectthe position including accelerometers, inertial measurement units, orinductive sensors.

FIG. 16 is a flow chart of a method 1600 for measuring power transmittedto a drivetrain, according to some embodiments. Although method 1600 isdescribed in conjunction with the systems of FIGS. 1-6 and 15, anysystem that performs method 1600 is within the scope and spirit ofembodiments of the techniques disclosed herein. In one embodiment, powermeasurement system 200 of FIG. 2A, is configured to perform method 1600.Programming instructions for performing method 1600 are stored in anon-transitory computer readable storage medium and executed by aprocessing unit within power measurement system 200. In one embodiment,the programming instructions comprise a computer program product. In oneembodiment, the programming instructions are stored on a non-transitory,non-volatile memory device coupled to logic board 207 and executed by amicroprocessor coupled to logic board 207.

Method 1600 begins at step 1610, where power measurement system 200samples one or more vertical bearing reaction values (e.g., verticalbearing reaction 1303). In one embodiment, electrical analog signalsfrom load sensors 208 are sampled by ADC 1504 to generate correspondingADC samples. The ADC samples are used as input values to a sensorcalibration curve, with force values provided as corresponding outputs.In certain embodiments, sensor amplifier and filter 1505 amplifiesand/or filters the electrical analog signals to generate processedanalog signals to be digitized by ADC 1504.

As described herein, sensor calibration curves can be implemented usinglookup tables or calibration functions (with curve-fit coefficients). Inone embodiment, a temperature value is also sampled (e.g., fromtemperature sensor 1506) and used for temperature compensation of thesensor calibration curves.

At step 1612, power measurement system 200 measures one or morerotational position values (e.g., of crank spindle 210) as describedherein. In one embodiment, a rotational position value of crank spindle210 indicates a rotational position value of crank arms 101. Magnets 212are positioned to pass by Hall Effect sensor 301 as crank spindle 210changes rotational position, indicating that crank spindle 210 is in oneof a fixed number of sectors of rotation. In one embodiment, eightmagnets 212 are used and eight sectors (octants) are detected asdiscrete rotational position values. A rotational position value betweenthe discrete rotational position values can be calculated byinterpolation for a specific time between two previously recordedrotational position value changes, based on a time interval betweenrotational position value changes and the specific time required forsampling a rotational position. In other embodiments, alternativerotational position sensing is implemented using either incremental ordirect measurement techniques.

At step 1614, power measurement system 200 calculates torque valuesapplied through crank arms 101. In one embodiment, power measurementsystem 200 calculates torque values according to Equation 2. In anotherembodiment, power measurement system 200 calculates torque valuesaccording to Equation 3.

At step 1616, power measurement system 200 calculates rotationalvelocity values. In one embodiment, time passage intervals are measuredbetween magnets 212 passing by Hall Effect sensor 301, and discreterotational velocity values are calculated as a direct function (e.g.,reciprocal) of the time passage intervals. Interpolation between thediscrete rotational velocity values can be used to estimate a rotationalvelocity value at a specific time. In alternative embodiments, differenttechniques can be implemented to detect and/or calculate rotationalvelocity.

At step 1618, power measurement system 200 calculates power values. Inone embodiment, power measurement system 200 calculates power valuesaccording to Equation 1 for power transmission from a cyclist to abicycle.

At step 1620, power measurement system 200 transmits one or more powervalues calculated in step 1618. In one embodiment a user interfacedevice 1501 is configured to receive and display the one or more powervalues.

In certain embodiments, power measurement system 200 transmits measuredpower values and/or other data to a user interface device, such as userinterface device 1501. In certain embodiments, power measurement system200 transmits measured sensor data to user interface device 1501,instead calculates power using the measured sensor data.

For clarity, the description herein refers to drive side and non-driveside components and measuring forces at the drive side. However, thedisclosed techniques for measuring at the drive side also apply to thenon-drive side of power measurement system 200. More generally,components referred to herein with respect to the drive side can beconsidered to be disposed at a measurement side of power measurementsystem 200. In one embodiment, the measurement side is the drive sideand a measurement side inner bearing cup is drive side inner bearing cup202, a measurement side outer bearing cup is drive side outer bearingcup 204, and a measurement side bottom bracket bearing is drive sidebottom bracket bearing 201. In an alternative embodiment, themeasurement side is the non-drive side and a measurement side innerbearing cup is a non-drive side inner bearing cup, a measurement sideouter bearing cup is a non-drive side outer bearing cup, and ameasurement side bottom bracket bearing is non-drive side bottom bracketbearing 211. In this alternative embodiment, components associated withperforming physical measurements can be positioned at the non-driveside.

An open volume between measurement side outer bearing cup andmeasurement side inner bearing cup can contain air or any othercompressible or deformable solid material. In general, calibration ofpower measurement system 200 can account for force transfer through thesolid material. Furthermore, the measurement side outer bearing cup andmeasurement side inner bearing cup can be fabricated in a form thatincludes any technically suitable open volume geometry (e.g., circular,square, octagonal, etc.), while preserving a circular geometry formounting the measurement side bottom bracket bearing.

In summary, techniques are disclosed for measuring power transmittedfrom a cyclist to a bicycle through crank arms. The techniquesindirectly measure power values for power transmitted through the crankarms using directly measured physical values for vertical bearingreaction force, rotational position, and rotational velocity. Thedirectly measured physical values are sampled from sensors that do notrotate or move with respect to a bicycle frame. The sensors are easilypackaged within a bicycle bottom bracket shell.

The disclosed systems and methods have been explained above withreference to several embodiments. Other embodiments will be apparent tothose skilled in the art in light of this disclosure. Certain aspects ofthe described method and apparatus may readily be implemented usingconfigurations other than those described in the embodiments above, orin conjunction with elements other than those described above. Forexample, different algorithms and/or logic circuits, perhaps morecomplex than those described herein, may be used.

Further, it should also be appreciated that the described systems andmethods can be implemented in numerous ways, including as a process, anapparatus, or a system. The methods described herein may be implementedby program instructions for instructing a processor to perform suchmethods, and such instructions recorded on a non-transitory computerreadable storage medium such as a hard disk drive, floppy disk, opticaldisc such as a compact disc (CD) or digital versatile disc (DVD), flashmemory, etc., or communicated over a computer network wherein theprogram instructions are sent over optical or electronic communicationlinks. It should be noted that the order of the steps of the methodsdescribed herein may be altered and still be within the scope of thedisclosure.

It is to be understood that the examples given are for illustrativepurposes only and may be extended to other implementations andembodiments with different conventions and techniques. While a number ofembodiments are described, there is no intent to limit the disclosure tothe embodiment(s) disclosed herein. On the contrary, the intent is tocover all alternatives, modifications, and equivalents apparent to thosefamiliar with the art.

In the foregoing specification, the invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the invention is not limited thereto. Variousfeatures and aspects of the above-described invention may be usedindividually or jointly. Further, the invention can be utilized in anynumber of environments and applications beyond those described hereinwithout departing from the broader spirit and scope of thespecification. The specification and drawings are, accordingly, to beregarded as illustrative rather than restrictive. It will be recognizedthat the terms “comprising,” “including,” and “having,” as used herein,are specifically intended to be read as open-ended terms of art.

1. A system, comprising: a measurement side inner bearing cup having anoutside diameter, configured to fit within a measurement side outerbearing cup having an inside diameter, wherein an open volume is formedbetween the outside diameter of the measurement side inner bearing cupand the inside diameter of the measurement side outer bearing cup; afirst load sensor, coupled to the measurement side inner bearing cup ata first position along the outside diameter and within the open volume,wherein the first load sensor is configured to provide a first analogelectrical signal responsive to an applied force; an analog-to-digitalconverter configured to sample the first analog electrical signal intocorresponding digital values; and a processor coupled to theanalog-to-digital converter and configured to: generate a set of forcevalues using a first set of the digital values; generate a rotationalvelocity value using a second set of the digital values; calculate atorque value by using the set of force values; and calculate a powervalue by multiplying the torque value with the rotational velocityvalue.